Characterization of power induced heating and damage in fiber optic probes for near-field scanning optical microscopy

Near-field scanning optical microscopy for high-resolution membrane studies

The desire to directly probe biological structures on the length scales that they exist has driven the steady development of various high-resolution microscopy techniques. Among these, optical microscopy and, in particular, fluorescence-based approaches continue to occupy dominant roles in biological studies given their favorable attributes. Fluorescence microscopy is both sensitive and specific, is generally noninvasive toward biological samples, has excellent temporal resolution for dynamic studies, and is relatively inexpensive. Light-based microscopies can also exploit a myriad of contrast mechanisms based on spectroscopic signatures, energy transfer, polarization, and lifetimes to further enhance the specificity or information content of a measurement. Historically, however, spatial resolution has been limited to approximately half the wavelength due to the diffraction of light. Near-field scanning optical microscopy (NSOM) is one of several optical approaches currently being developed that combines the favorable attributes of fluorescence microscopy with superior spatial resolution. NSOM is particularly well suited for studies of both model and biological membranes and application to these systems is discussed.

Quantification of electron-phonon scattering for determination of temperature variations at high spatial resolution in the transmission electron microscope

This work investigates the quantification of electron-phonon thermal diffuse scattering (TDS) for detection of temperature variations with nanometer spatial resolution in transmission electron microscopy (TEM). Observations of TDS intensity for (100) single crystal Si and Ge show interdependences of temperature and sample thickness which can be understood through the angular distributions of electron-phonon scattering as a function of temperature. The temperature sensitivity of the integrated TDS intensity can be of the order of 10(-3) K(-1) for Si and Ge. This shows that measurement of the TDS intensity in the TEM is a promising means for nanoscale temperature measurement; our measurements to date have demonstrated that temperature changes as small as 5 K are detectable.

Optical-force-induced artifacts in scanning probe microscopy

In the practice of near-field scanning probe microscopy, it is typically assumed that the distance regulation is independent of the optical signal. However, we demonstrate that these two signals are entangled due to the inherent action of optically induced force. This coupling leads to artifacts in both estimating the magnitude of optical fields and recording topographic maps.

Material ejection and redeposition following atmospheric pressure near-field laser ablation on molecular solids

Near-field laser ablation (NF-LA) coupled with mass spectrometry (MS) is very promising for highly spatially resolved chemical analyses on various substrates at atmospheric pressure, for example, in materials and life science applications. Although nanoscale sample craters can be produced routinely, no molecular mass spectra of ablated material from craters of <or=1 microm diameter have ever been acquired by NF-LA MS at atmospheric pressure. Some of the pressing questions are thus how much of the ablated material is transported into the mass spectrometer and in what form. Therefore, material redeposition on the near-field tip's surface from laser ablation of molecular solids was characterized with scanning electron microscopy. The crater profiles were studied by scanning probe microscopy. The results shown in this study demonstrate that there could be as much as 70% of the ablated material deposited on the near-field tip's surface. The redeposited products were found to be confined to a height of approximately 50 microm, thus suggesting that most components inside near-field ablation plumes propagate about the same distance for both anthracene and tris(8-hydroxyquinolinato)aluminum. Nanoparticles ablated from craters of <or=1 microm diameter are clearly observed. Furthermore, observation of tips after ablation of an anthracene surface angled at 60 degrees with respect to a horizontal surface shows that the direction of the near-field ablation plume is neither in the direction of the surface normal nor towards the axis of incident laser beam but deflected further away from surface normal.